Vacuum Modulated EGR System

With this system, the amount of exhaust gas admitted into the intake manifold depends on a vacuum signal (ported vacuum), controlled by throttle position.

When the throttle is closed (at idle or deceleration), there is no vacuum signal to the EGR valve because the EGR vacuum port is above the closed throttle valve. As the throttle valve is opened, a ported vacuum signal is supplied to the EGR valve, admitting exhaust gas into the intake manifold.